Flame retardant compositions

ABSTRACT

A silicone elastomer stock which exhibits improved flame resistance in the cured state consists essentially of a silicone elastomer, a filler, a small amount of a flame retardant material selected from the group consisting of platinum and platinum compounds and a Group II metal oxide.

United States Patent 1191 Pfeifer et al. 1 Jan. 16, 1973 [54] FLAMERETARDANT COMPOSITIONS 2,575,687 11 1951 Simon et al. ..260/37 SB xInventors: Charles w. Pieifer, S y, 3,261,801 7/l966 Wormuth ..260/37 SBN.Y.; William J. Bobear, Latham, QTHER TIO both of NY. I I Oleesky;Handbook of Remforced Plastics, Reinhold Asslgheei General Electric p yPublishing Corp.; 1964; page 460; Sci Lib., TA 22 Filed: Sept. 4, 1970455-P55 1 pp 69,982 Primary Examiner-Lewis T. Jacobs Att0rneyD0nald J.Voss, Donavon L. Favre, Frank 52 US. (:1. ..260/375 B, 260/DlG. 24Neuhause Oscar wadde" and Joseph 51 1111.0. ..C08g 51/04 58 Field ofSearch.....260 37 SB, 46, 75 R, DIG. 24 l [57] 7 ABSTRACT ReferencesCited A silicone elastomer stock which exhibits improved Y flameresistance in the cured state consists essentially v UNITED STATESPATENTS of a silicone elastomer, a filler, a small amount of 213,514,424 5/1970 Noble et al ..260/37 SB lame etardant material selectedfrom the group con- 3,269,981 8/1966 Goossens ...260/37 SBX sisting ofplatinum and platinum compounds and a 3,137,670 6/1964 Maneri ..260/37SB Group [I metal oxide, 3,468,838 9/1969 Loraine et al ..260/37 SB3,539,530

Karstedt ..260/37 SB X 11 Claims, N0 Drawings FLAME RETARDAN'ICOMPOSITIONS BACKGROUND OF THE INVENTION This invention relates toorganopolysiloxane compositions having improved flame retardantproperties. More particularly, this invention is concerned with acomposition of mater which, in the cured state, exhibits improved flameretardant properties and which comprises (l) organopolysiloxane gumconvertible to the cured solid, elastic state and consisting essentiallyof silicon atoms, oxygen atoms and organic groups selected from theclass consisting of methyl radicals, aromatic radicals selected from theclass consisting of aryl and halogenated aryl radicals, vinyl radicals,lower alkyl radicals, lower cyanoalky] radicals and lower haloalkylradicals, (2) a finely divided inorganic filler, (3) a platinum compoundor platinum and (4) a Group II metal oxide.

A method for improving the flame retardancy of a silicone rubber isshown in U.S. Pat. No. 3,514,424, Noble et al., where a platinumcompound or platinum is combined with other components of a siliconerubber to impart flame retardancy. While the addition of platinum orplatinum compound does improve the flame retardancy of silicone rubbersand is entirely adequate for most uses, the rubbers produced accordingto the Nobel et al. patent lack, to a degree, h'eat reversion resistancewhen a high platinum level is employed, and they are not as flameretardant as might be desired in some applications.

SUMMARY In accordance with the present invention, it-has been discoveredthat by incorporating a small amount of a Group II metal oxide,preferably zinc oxide, in combination with a platinum compound orplatinum in a filled silicone rubber composition that the flameretardancy of the silicone rubber is markedly improved.

DESCRIPTION OF THE PREFERRED EMBODIMENTS The organopolysiloxane which isconvertible to the cured, solid, elastic state can be any of theorganopolysiloxane gums known in the art which fall within thecomposition range stated above and have a viscosity of from about5,000,000 to 50,000,000 centistokes. These organopolysiloxanes areadvantageously obtained by condensing a diorganodihydrolyzable silane,for example, dimethyldichlorosilane with or without small amounts ofmonoorganotrihydrolyzable silanes or trimganom onohydroly'zable silanes,for example methyltrichlorosilane, trimethylchlorosilane, etc., andthereafter effecting condensation 'of the hydrolysis product using acondensing agent, for instance, an alkaline condensing agent, such aspotassium hydroxide, sodium hydroxide, etc.,'or an acidic condensingagent, such as ferric' chloride, etc. Alternately, cyclic polymers ofdimethylsiloxane can be condensed with an alkaline condensing agent togive the desired organopolysiloxane which is convertible to the cured,solid, elastic state. Whatever the method of formulation of theconvertible organopoly-siloxane, the final material can contain up to 35mole per cent of phenyl radicals bonded by silicon-carbon links and upto 2 percent of vinyl radicals bonded through silicon-carbon links.Thus, when the convertible material is formed by hydrolysis a portion ofthe starting material can be diphenyldihydrolyzable silane,methylphenyldihydrolyzable silane, f methylvinyldihydrolyzable silane,divinyldihyrolyzable silane, etc., or the monoorganotrihydrolyzable ortriorganomonohydrolyzable silanes containing these radicals.

It is essential to the production of truly flame retardant compositionsthat a quantity of a filler be present. -In general, any filler systemwhich is residually non-alkaline, i.e., acid or neutral, can beemployed. Any of the finely divided silica fillers generally used forsilicone rubber, such as silica aerogel, fumed silica ground quartz, andfinely divided silica treated with organosilicon materials, e.g.,trimethylchlorosilane, etc., can be employed. The treatment of silicafillers with organosilicon materials are as described, e.g., in U.S.Pat. Nos. 2,938,009Lucas and 3,004,859-Lichtenwalner. The amount offiller present can vary within wide ranges, from 10 to 300 parts offiller per 100 parts of the organopolysiloxane gum. Preferably, thefiller is present in an amount of from 40 to 125 parts per 100 parts ofthe organopolysiloxane gum. Up to about twothirds of the total silicafiller can be replaced by such materials as carbon black, titaniumdioxide, or diatomaceous earth, or a combination of these materials, solong as a residual alkalinity in the filler system does'not result.However, while clay has often been employed as a filler for siliconerubber, it has unexpectedly been found that convertibleorganopolysiloxane materials filled with alkaline clay, alone, do notexhibit the flame retardancy shown by the materials filed with a finelydivided silica or a mixture of silica with one or more of the othermaterials mentioned previously.

Any of the residually non-alkaline metal oxides of Group II may be usedto replace the filler in whole or in part. The preferable fillerreplacement material is zinc oxide.

The platinum-containing material which is used is, as previouslymentioned, any of the materials generally utilized in SiH+Si-olefinreactions. Among the forms of this platinum are elemental platinum asshown in U.S. Pat. No. 2,970,lBailey and platinum-on-charcoal,platinum-on-gamma-alumina, platinum-on-silica gel, platinum-on-asbestos,and chloroplatinicacid,

as mentioned in US. Pat. No. 2 ,82 3,2l8-Speier.

Further, the platinum-containing material can be selected from thosehaving the formulQ PtG; 611255). and H(PtCl3-o1efin), as described inU.S. Pat. No. 3,159,601 Ashby. The olefin shown in the previous twoformulas can be almost any type of olefin, but is preferably an alkenehaving from two to eight carbon atoms, a cycloalkene having from five toseven carbon atoms or styrene. Specific olefins utilizable in the aboveformulas are ethylene propylene, the various moles per gram of platinumof a member selected from the class consisting of alcohols, ethers,aldehydes and mixtures of the above as described in US. Pat. No.

3,220,972Lamoreaux.

The preferred platinum compound to be used as a flame retardant additiveis that disclosed in French Pat. No. 1,548,775 of Karstedt. Generallyspeaking, this type of platinum complex is formed byreactingchloroplatinic acid containing 4 molecules of water of hydration withtetra-methyl-tetravinylcyclotetrasiloxane in the presence of sodiumbicarbonate in an ethanol solution.

A large number of other platinum compounds, including. complexes whichare conventionally and generally widely known in the field, ofSil-Lolefin addition reactions are also useful in the practice of thepresent invention.

Small but effective amounts of the platinum compound are sufficient toimpart the desired flame retardancy to the siliconerubber. In general,amounts of from less than one to more than 250 parts per million asplatinum based on the organopolysiloxane gum can be used. Preferably,the amount is-from less than 1 ppm to about 25 ppm as platinum based onthe organopolysiloxane gum. When the gum is a methyl andphenyl-containing gum, it is preferable that less than 1 ppm of platinumbe used in order to prevent damage due to heat aging of the finalproduct.

The platinumor platinum compound can be employed in amounts greater than250 parts per million but due to the cost of the materials, utilizationof greater than 250 ppm is not preferred as the increased amounts'do notprovide significant improvement in the flame retardancy of the finalmaterial.

It is particularly surprising that the presence of a Group 11 metaloxide, particularly zinc oxide, should be found in conjunction with theplatinum or platinum compound to enhance the flame retardancy impartedby the platinum or platinum compound.

The Group 11 metal oxides which may be employed in the practice of thepresent invention include beryllium oxide, magnesium oxide, calciumoxide, strontuim oxide, barium oxide, radium oxide, zinc oxide, cadmiumoxide, and mercuric oxide. The amounts as each of the oxides to be addedvaries with the alkalinity of the oxide. Zinc oxide, the preferredmaterial, is preferably added in an amount of from 1 to 15 parts perhundred partsbased upon 100 parts of gum. This amount, however, can varyfrom a small but effective amount, less than 1 part to. greater than 100parts, per 100 parts of gum. Magnesium oxide is preferably employed inthe range of 0.1 to 1.0, .such as 0.4 part per 100 parts of gum. his notrecommended that greater than 1 part of magnesium oxide be employed.Magnesium oxide is generally employed in a concentration of 0.2 to 0.6part. Zinc oxide, on the other hand, is employed generally in aconcentration of about 1 to about 100 parts and preferably about 1 toabout 15 parts, per 100 parts of gum.

While the previously described organopolysiloxane gum, silica filler orcombination of silica filler with others of the enumerated fillers, andplatinum-containing material andGroup 11 metal oxide are essential to2,890,188-Konkle et al. Additionally, resinous organopolysiloxanematerials such as those formed from tetrafunctional alkysilicates,triorganomonofunctional silanes, and, in some cases, difunctionaldiorganosilanes, as disclosed and claimed in U.S. Pat. No.2,857,356-Goodwin, Jr., can also be employed.

The order of addition of the various components to the composition isimmaterial. All can be added simultaneously or the Group 11 metal oxideand filler, the platinum compound or platinum and additional materialswhen they are present can be added at varying times to theorganopolysiloxane gum and a homogeneous blend obtained. Followingblending of the various materials, the material is cured using any ofvarious curing agents as, for example, benzoyl peroxide, tertiary butylperbenzoate, bis-(2,4-dichlorobenzoyl)peroxide, etc. These curing agentscan be present in varying amounts ranging from about 0.3 percent to ashigh as 6 to 10 percent by weight, or more, based on the weight of theorganopolysiloxane gum. Further, the convertible organopolysiloxane gumcan be cured by any other method'known in the art without adverselyaffecting the flame retardant properties imparted by the filler andplatinum-containing material. Cure is accomplished v with the variousperoxide andv perbenzoate catalysts by heating with slight pressure atfrom about 100C to 200C for times ranging from 5 to 15 minutes. Inaddition to, or instead of this press cure, the silicone rubbercomposition can be treated at temperatures of from about 200C to 500Cfor sufficient time to assure complete conversion of the polysiloxanegum to a substantially infusible and insoluble state.

The process of the present invention will now be more fully illustrated.These illustrations should not be considered as limiting in any way thefull scope of the present invention as covered in the appended claims.

The platinum compound which was used to impart flame retardancy in therubbers produced in thefollowing examples was produced by the followingprocedure. Into a reaction vessel was placed 74 parts oftetravinyltetramethylcyclotetrasiloxane, 4.5 parts of sodium bicarbonateand the reaction vessel was purged with nitrogen gas for 15 minutes anda nitrogen blanket was maintained over the reaction mixture throughoutthe process. Then, 3.7 parts of chloroplatinic acid containtheproduction of the flame retardant silicone rubber composition, othermaterials can be added without iming 4 molecules of water of hydrationand 17.8 parts of ethanol were added. The mixture was slowly heated to Cwith vigorous agitation and held at 55C for 30 to 45 minutes. Themixture was then refluxed for 15 to 30 minutes. A reaction product whichformed was then vacuum stripped and filtered.

EXAMPLE 1 A formulation was prepared containing a dimethylvinylchain-stopped polydiorganosiloxane gum having a viscosity of 15 X 10centistokes and containing 5.3 mole per cent methylphenylsiloxy units,0.2 mole per cent of methylvinylsiloxy units and the remainderdimethylsiloxy units and containing vinyl groups on the terminal siloxyunits, 35 parts fumed silica, 5 parts of octamethylcyclotetrasiloxane, 7parts of a methoxystopped polymer having a viscosity of centistokes,0.333 part of the silanol-stopped fluid having a viscosity of 40centistokes and 0.246 part of a solution containing 1 part of theabove-described platinum complex dissolved in 10 parts of a vinylchain-stopped silicone oil having a viscosity of about 10 centistokes.The formulation was divided into two fractions. To one fraction wasadded parts of zinc oxide product No. XX- 78 obtained from the NewJersey Zinc Company.

Both fractions were catalyzed with a 50% solution of dichlorobenzoylperoxide in a silicone oil having a viscosity of 1,000 centistokes. Bothfractions were then press-cured, baked at 1 hour at 400F and then testedby holding a strip of the rubber formed edgewise threefourths inch abovea Bunsen burner top in a 1% inch high flame for 12 seconds after whichthe extinguishing time in seconds was recorded. The fraction containingthe zinc ozide had an extinguishing time of 4 seconds using a naturalgas blue flame at 2,000F. The rubber produced by the reaction containingnozinc oxide had an extinguishing time of 10 seconds using identicalconditions.

EXAMPLES 2, 3, 4, 5, 6 and 7 The following table shows the results ofadding various quantities of zinc oxide to the same gum formulationoutlined in Example 1. The peroxide catalyst used in Examples 2 through7 was the same, dissolved in the same solvent as was used in Example 1.

EXAMPLE 8 A' silicone rubber was made using the following formulation.The formulation contained 100 parts of a vinyl chain-stoppedpolydimethylsiloxane gum having a viscosity of 40,000,000, 3 parts of a10 centistoke methoxy-stopped polydimethylsiloxane fluid, 4 parts of asilanol-stopped polydimethylsiloxane fluid having a viscosity of 40centistokes, 37 parts of a fumed silica, 0.25 parts of the platinumcomplex solution of Example 1, parts of Cadox XX-78 zinc oxide and 1.2parts of the dibenzoyl peroxide catalyst dissolved in silicone oildescribed in Example 1. The formulation was presscured using a catalyst,1.2 parts of a composition containing benzoyl peroxide and apolydimethylsiloxane fluid having a viscosity of C at 1,300 centistokes.The rubber produced was tested by holding a strip edgewise three-fourthsinch above a Bunsen burner top and a 1% inch high propane luminous flamefor 12 seconds. The extinguishing time was 19 seconds.

EXAMPLE 9 Example l was repeated with the exception that 0.4 part ofmagnesium oxide was added to the gum instead of the zinc oxide. Theflame retardancy of the rubber produced using this formulation using apropane flame at 1480F had a self-extinguishing time of 9 seconds.

While the foregoing examples have of necessity been directed only to afew of the composition variables which are practicable in the practiceof the present invention, it should be understood, however, that manyother variables are within the scope of the present invention. The gumsinto which the synergistic flame retardant composition is added are notby necessity limited only to those specifically enumerated in theexamples and may include all of the gums commonly used in themanufacture of silicone rubber. These gums includecyanoalkyl-substituted polysiloxanes and fluoroalkyl-substitutedpolysiloxanes, among others.

Having thus described the invention, what we desire to secure and claimby the United States patent is:

1. A composition of matter which in a cured state exhibits improvedflame-retardant properties, the composition comprising:

1. parts of an organopolysiloxane gum convertible to the cured, solid,elastic state and consisting essentially of silicon atoms, oxygen atoms,and or ganic groups selected from the class consisting of methylradicals, aromatic radicals selected from the class consisting of aryland halogenated aryl radicals in an amount of from O to 35 mole per centof the organic groups, and from 0 to 2 mole per cent of the totalorganic groups of vinyl radicals, there being from 1.98 to 2.05 organicgroups per silicon atom,

a finely divided, non-alkaline inorganic filler in an amount of from 10to 300 parts, by weight,

3. small, but effective amount to impart flame retardance of a platinumcontaining material not exceeding 250 parts per million by weight basedon the organopolysiloxane gum, and

4. a small but effective amount to improve flame retardancy of the abovecomposition of a Group 11 metal oxide not to exceed 100 parts by weightbased on the organopolysiloxane gum.

2. The cured product of claim 1 3. The composition of claim 1 furthercharacterized by the inorganic filler being present in an amount of from40 to parts.

4. The composition of claim 1 further characterized by theplatinum-containing material being present in a range to provide fromabout 1 to about 25 parts per million, by weight based on theorganopolysiloxane gum, of platinum.

5. The composition of claim 1 further characterized by thephenyl-to-silicon ratio being from about 0.01 to about 0.4.

6. The composition of claim 1 further characterized by the ratio ofphenyl to-silicon being from about 0.03 to about 0.1

7. The composition of claim 1 further characterized by the inorganicfiller being fumed silica and the Group 11 metal oxide being zinc oxide.

8 The composition of claim 7 further characterized by the zinc oxidebeing present in an amount of from 1 to 15 parts.

9. The composition of claim 1 further characterized by from 0.01 to 1part of magnesium oxide being present.

10. The composition of claim 1 further characterized by the ratio ofphenyl groups to silicon in the polysiloxane being from about 0.01 toabout 0.08.

11. A composition of matter which in a cured state exhibits improvedflame-retardant properties, the composition comprising:

1. 100 parts of an organopolysiloxane gum convertible to the cured,solid, elastic state and consisting essentially of silicon atoms, oxygenatoms, and organic groups selected from the class consisting of loweralkyl, cyano lower alkyl, and halo lower alkyl radicals in an amount offrom to 35 mole a finely divided, non-alkaline inorganic filler in anamount of from 10 to 300 parts, by weight,

. small, but effective amount to impart flame retardancy of a platinumcontaining material not exceeding 250 parts per million by weight basedon the organopolysiloxane gum, and

. a small but effective amount to improve flame retardancy of the abovecomposition of a Group ll metal oxide not to exceed parts by weightbased on the organopolysiloxane gum.

2. The cured product of claim
 1. 2. a finely divided, non-alkalineinorganic filler in an amount of from 10 to 300 parts, by weight,
 2. afinely divided, non-alkaline inorganic filler in an amount of from 10 to300 parts, by weight,
 3. small, but effective amount to impart flameretardancy of a platinum containing material not exceeding 250 parts permillion by weight based on the organopolysiloxane gum, and
 3. small, buteffective amount to impart flame retardance of a platinum containingmaterial not exceeding 250 parts per million by weight based on theorganopolysiloxane gum, and
 3. The composition of claim 1 furthercharacterized by the inorganic filler being present in an amount of from40 to 125 parts.
 4. The composition of claim 1 further characterized bythe platinum-containing material being present in a range to providefrom about 1 to about 25 parts per million, by weight based on theorganopolysiloxane gum, of platinum.
 4. a small but effective amount toimprove flame retardancy of the above composition of a Group II metaloxide not to exceed 100 parts by weight based on the organopolysiloxanegum.
 4. a small but effective amount to improve flame retardancy of theabove composition of a Group II metal oxide not to exceed 100 parts byweight based on the organopolysiloxane gum.
 5. The composition of claim1 further characterized by the phenyl-to-silicon ratio being from about0.01 to about 0.4.
 6. The composition of claim 1 further characterizedby the ratio of phenyl-to-silicon being from about 0.03 to about 0.1 7.The composition of claim 1 further characterized by the inorganic fillerbeing fumed silica and the Group II metal oxide being zinc oxide. 8 Thecomposition of claim 7 further characterized by the zinc oxide beingpresent in an amount of from 1 to 15 parts.
 9. The composition of claim1 further characterized by from 0.01 to 1 part of magnesium oxide beingpresent.
 10. The composition of claim 1 further characterized by theratio of phenyl groups to silicon in the polysiloxane being from about0.01 to about 0.08.
 11. A composition of matter which in a cured stateexhibits improved flame-retardant properties, the compositioncomprising: